This invention relates to assaying material properties.
In the automatic assay of cotton using HVI/HVT equipment it is necessary to calibrate the equipment periodically using a standard cotton sample prepared by a standards institute, namely the U.S. Department of Agriculture.
In order to perform an assay on a shipment of cotton, samples are taken from the shipment and subjected to the assay routines built into the HVI/HVT equipment, these routines including length, uniformity, strength and so on. For calibration purposes, the same routines are performed on the standard cotton supplied by the USDA. The equipment automatically adjusts its internal parameters (or in some older equipment those internal parameters may have to be manually adjusted) to correspond to the standard values of the sample, which are supplied by the USDA along with the sample.
This way of working, which, on the face of it appears to be perfectly rational, has been an internationally agreed--not to mention mandatory-procedure for some considerable period of time. The internationally recognised standard is controlled by the USDA and its sample cotton is ubiquitous. The importance of the assay procedure is that the price and often the suitability of the cotton is determined by it. Clearly, if the price is wrong, somebody loses something, which may be marginal; if the end use is wrong, the resulting loss may be substantially greater in that faulty goods may be very expensively produced wasting the entire batch of cotton.
In most testing houses, calibration is carried out at least once, often twice a day; in the USDA's testing establishment, calibration is carried out much more frequently in order to try to ensure the highest degree of accuracy.
The present invention is based on the problem that, notwithstanding the efforts made to ensure accuracy using the mandatory calibration procedure and the USDA standard sample, there is usually variable correlation between the assay results of different testing houses, and indeed usually, on an inter-house comparison basis, a significant number of testing houses (not, in different instances, the same houses) cannot differentiate between different standard samples, for example between standard strong and standard weak cottons.
This problem is usually ascribed to differences in operator procedures or techniques, differences in humidity and other uncontrollable or uncontrolled variables, and the concensus of opinion in the trade is that these problems are unavoidable.
However, we have now found that the problems do not reside in such areas as has hitherto been supposed, and we have also found that the problems are by no means unavoidable.